The response of rabbit lymphocytes to different stimuli will be explored further in particular regard to a comparison of stimulation of proliferation to stimulation of immunoglobulin synthesis. A simplified assay employing protein A is being developed to measure incorporation of radiolabeled amino acids with immunoglobulins. The T cell requirement for anti-Ig or con A stimulation of Ig synthesis will be determined and the role of T cells as helper or suppressors of Ig synthesis explored. The expression of immunoglobulin allotypes is being examined in vitro using an inhibition and enhancement of plaque forming cells by anti-allotypic reagents. The effect of allotypic suppression on the expression of other allotypic determinants in vitro is also being examined.